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Mission typeNavigation
OperatorUS Air Force
COSPAR ID1993-032A[1]
SATCAT no.22657[1]
Mission duration7.5 years (planned)[2]
Spacecraft properties
Spacecraft typeGPS Block IIA[2]
Launch mass1,816 kilograms (4,004 lb)[2]
Start of mission
Launch date13 May 1993, 00:07:00 (1993-05-13UTC00:07Z) UTC
RocketDelta II 7925-9.5, D220[3]
Launch siteCape Canaveral LC-17A[3]
End of mission
DisposalPlaced in a graveyard orbit
Deactivated18 March 2016 (2016-03-19)
Orbital parameters
Reference systemGeocentric
RegimeMedium Earth
Perigee altitude20,033 kilometres (12,448 mi)[4]
Apogee altitude20,327 kilometres (12,631 mi)[4]
Inclination54.9 degrees[4]
Period717.88 minutes[4]

USA-91, also known as GPS IIA-11, GPS II-20 and GPS SVN-37, was an American navigation satellite which formed part of the Global Positioning System. It was the eleventh of nineteen Block IIA GPS satellites to be launched.

USA-91 was launched at 00:07:00 UTC on 13 May 1993, atop a Delta II carrier rocket, flight number D220, flying in the 7925-9.5 configuration.[3] The launch took place from Launch Complex 17A at the Cape Canaveral Air Force Station,[5] and placed USA-91 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-37XFP apogee motor.[2]

On 14 June 1993, USA-91 was in an orbit with a perigee of 20,033 kilometres (12,448 mi), an apogee of 20,327 kilometres (12,631 mi), a period of 717.88 minutes, and 54.9 degrees of inclination to the equator.[4] It broadcast signal PRN 07, and operated in slot 4 of plane C of the GPS constellation.[6] The satellite had a mass of 1,816 kilograms (4,004 lb). It had a design life of 7.5 years,[2] and ceased operations on 20 December 2007.

Following decommissioning, it was kept as a reserve satellite. It was finally put in a disposal orbit approximately 1000 km above the operational constellation on March 18, 2016.[7]


  1. ^ a b "Navstar 2A-11". US National Space Science Data Center. Retrieved 10 July 2012.
  2. ^ a b c d e f Krebs, Gunter. "GPS-2A (Navstar-2A)". Gunter's Space Page. Retrieved 10 July 2012.
  3. ^ a b c McDowell, Jonathan. "Launch Log". Jonathan's Space Page. Retrieved 10 July 2012.
  4. ^ a b c d e McDowell, Jonathan. "Satellite Catalog". Jonathan's Space Page. Retrieved 10 July 2012.
  5. ^ McDowell, Jonathan. "Launch List". Launch Vehicle Database. Jonathan's Space Page. Retrieved 10 July 2012.
  6. ^ Wade, Mark. "Navstar". Encyclopedia Astronautica. Retrieved 10 July 2012.
  7. ^ "50 SW to dispose of two GPS satellites". United States Air Force. Retrieved 21 March 2016.